Gas-Solid Contacting in Kilns, Moving Beds, and Cyclones

6 Gas-Solid Contacting in Kilns, Moving Beds, and Cyclones 

In this section we shall present a brief description of gas-solid contacting in kilns, moving beds, cyclones, and transfer line reactors. A substantial number of gas-solid reactions are carried out in equipment of this type, such as ironmaking in the blast furnace (moving bed), the manufacture of cement (kilns), and certain direct reduction processes of iron oxide (kilns or moving beds). 

In spite of the major economic importance of these operations, the fundamental aspects of flow patterns and heat and mass transfer in these systems have received very much less attention than for the case of beds and fluidized beds which were discussed in the preceding sections. This scarcity of information necessarily limits the material that can be presented here indeed the treatment of gas-solid reaction systems in kilns, moving beds, and cyclones will be based on the real (or assumed) analogy of these operations to packed-or fluidized-bed processing. 

Let us designate the length and the diameter of the kiln by L and D respectively, and let a be the angle formed by the kiln with the horizontal plane, co the number of times the kiln rotates per unit time, and (p the angle 

The mean residence time /r of the solids in the kiln may be estimated by using 

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